Interpretive Summary: The development and function of intramuscular fat cells is important to many species including pigs and cattle. Intramuscular and extramuscular fat tissue develop at different times and several enzyme and gene markers distinguish these two fat tissues in cattle and pigs. Understanding the ontogeny and regulation of intramuscular specific genes and marker enzymes would greatly enhance the potential to improve meat quality in meat animals.

Technical Abstract:
The cellular and metabolic aspects of developing intramuscular adipose tissue and other adipose tissue depots have been studied including examination of the expression of a number of genes. Depot dependent or depot “marker” genes such as stearoyl-CoA desaturase and leptin for subcutaneous adipose tissue and fatty acid-binding protein 4 and glucose-6-phosphate dehydrogenase for intramuscular adipose tissue have been identified. The regulation of intramuscular adipose tissue by many factors has been examined in several species. Additional studies are necessary to determine the ontogeny and importance of adipose tissue transcription factors and other regulatory factors as influenced by depot and species. Furthermore, there is little information on the ontogeny and regulation of expression of factors expressed and secreted by intramuscular adipocytes. Additionally, a number of factors from both skeletal muscle and adipose tissue appear to be responsible for communicating the energy needs and regulating energy availability between these two tissues. However, our limited knowledge of these factors, their interactions, and the interplay between adipose tissue and skeletal muscle limits the practical application to current animal production practices.